Raised Bed Soil Calculator & Soil Volume Guide
Buying too little soil means a second trip to the store mid-project; buying too much means bags sitting in the garage. Use the calculator below to get an exact volume for your bed, or check the reference table further down for common sizes.
Soil Volume Calculator
Soil volume: 7.5 cubic feet
Approx. bags needed: 5 bags
Estimate only — soil settles 5–10% after the first watering, so slightly overfilling is normal.
Soil Volume by Common Bed Size (Reference Table)
| Bed Size | Depth | Soil Volume | Approx. Bags (1.5 cu ft each) |
|---|---|---|---|
| 3' × 3' | 10" | ~7.5 cu ft | 5 bags |
| 2' × 6' (runner) | 17" | ~17 cu ft | 12 bags |
| 4' × 4' | 10" | ~13.3 cu ft | 9 bags |
| 3' × 6' | 10" | ~15 cu ft | 10 bags |
| 4' × 8' | 11" | ~29.3 cu ft | 20 bags |
For a bed size not listed here, use the calculator above, or the formula: length (ft) × width (ft) × depth (ft) = cubic feet.
What Mix to Use
A reliable, widely-used ratio for raised beds is 60% high-quality topsoil, 30% compost, and 10% aeration material (perlite or coarse sand). This gives you nutrient density from the compost, structure from the topsoil, and drainage from the aeration component — all three matter for raised beds specifically, since they drain faster than ground-level soil and need to hold both moisture and nutrients well.
A Few Things That Affect Your Actual Number
- Settling: Soil compacts 5–10% after the first watering and season. Fill slightly above the bed's rim initially rather than exactly level.
- Bag size varies by brand: Some are 1 cubic foot, others 1.5 or 2 — check the bag before you calculate your total (the calculator above lets you adjust this).
- Filling multiple beds: Buying soil in bulk (by the cubic yard) is usually more economical than bags once you're filling more than 2–3 standard-size beds — 27 cubic feet equals 1 cubic yard.
Ready to plan what goes where once the bed is filled? See our raised garden bed layout and planting ideas.
Shop our cedar raised garden bed, the Gro-Rite metal kit, or browse the full Yard & Garden collection. Deciding between materials? See our cedar vs. metal comparison.
